What is the difference between M4A and MP4 files? I am a bit confused.
This is the most popular question we get and seems to cause the most confusion to people new to MPEG 4 Audio. The existance of 2 different file extensions that can be used to represent MPEG 4 Audio files is unfortunate. MP4 files may or may not contain MPEG 4 Audio. If you see a M4A file you always know that it contains only MPEG 4 Audio<. MP4 can be used for MPEG 4 video files, combined video and audio files, or just plain MPEG 4 audio. Apple Computer started using and popularizing the M4A file extension to denote the file was an unprotected (non digital rights management) MPEG 4 Audio file. They did this because MP4 was too general (video, video/audio or audio) and might confuse some media players.

Now MPEG 4 Audio has its own file extensions, M4A, to avoid any possible problems with being confused with video files. It is recommended that you use the .m4a file extension rather than .mp4 on your audio files. Up until recently, there was much confusion among MP4/M4A encoder and player software. Some programs (Nero, Compaact) used .mp4 while others (WinAmp 5.02, Apple iTunes, iPod) used .m4a to denote MPEG 4 Audio files. Most software developers have now enabled a user selectable option in their software to allow you to choose the default file extension you wish to use to save MPEG 4 Audio files with. Almost all audio players will now play back files using either the .m4a or .mp4 file extension for maximum compatibility. After all, both the .m4a and .mp4 container file formats are the same, they just have different file extensions.

If your software program doesn't recognize your file extension, you can rename the file extension to the other one (i.e. m4a or mp4) and it should work.